I have a 96 tahoe and was wondering about the front ifs.  Is it possible to put manual locking hubs on this or no?  I saw all the toyotas and suzukis have them so why not?  

Why do you want to put manual locking hubs on your Tahoe? But i am sure that it can be possible to do. Pretty much anything is possible it just takes money. I have never been in favor of having manual locking hubs. Because its just another thing to break, and it also means if you forget to lock them in when you start the day then you will be crawling through the mud to lock them in when your stuck.  

How can you consider manual locking hubs as one more thing to break.  They are way more relaible than auto locking hubs. Sure it is nice to not have to get out and lock the hubs but when your auto locking hubs stop working your going to have a hard time trying to figure out what went wrong.  

heres a better option, if you are having trouble with it locking there is a manual engagement you can get instead of relying on the gas/electric switch.  

What is your reason for wanting manual hubs? If it is about engagement issues then mudb8 already answered. However if it is to stop front end drag of less moving parts then the answer is no. Milemarker, Warn, and Superwinch do not make anything in the manuual hubs for chevy after I believe 91. the toyotas and suzukis you saw had them either from the factory or through the above mentioned companies(up to 98 some 00-02's).